Each stage in a gas turbine engine includes a plurality of radially extending rotor blades, which are attached to a rotor disc. Near the radially inward portion of the rotor blades, adjacent to the rotor disc, the space between adjacent rotor blades may be filled by platforms integral to the respective rotor blades or by annulus fillers, which are separate from the rotor blades. Annulus fillers, by bridging the gap between the rotor blades, may define a radially inward airflow surface for air drawn through the gas turbine engine.